Figure 2.10. Enantiomers of 1-Bromo-1-ChloroethaneMCAT EXPERTISE
Whenever you see a carbon with four different substituents, think chirality.Two molecules that are nonsuperimposable mirror images of each other are called enantiomers.
Molecules may also be related as diastereomers. These molecules are chiral and share the same
connectivity, but are not mirror images of each other. This is because they differ at some (but not
all) of their multiple chiral centers.
Alternatively, a carbon atom with only three different substituents, such as 1,1-dibromoethane, has
a plane of symmetry and is therefore achiral. A simple 180° rotation around a vertical axis, as shown
in Figure 2.11, allows the compound to be superimposed upon its mirror image.